An example of a prior test clip for electronic devices, such as integrated circuits of the dual-in-line (DIP) package type, is disclosed in U.S. Pat. No. Re. 28,064. The DIP packages may have, for example, a total of from 14 to 64 leads arranged in a pair of parallel rows on the two generally relatively longer parallel sides of the DIP package, and typically the leads are spaced on 0.100 inch centers. The DIP package typically is used by soldering the leads into respective plated-through holes in a printed circuit board or by inserting the leads into a DIP socket already attached to a printed circuit board. For heat dissipation and possibly for other reasons, DIP packages ordinarily are spaced from each other and from other components on a printed circuit board at distances of at least several hundred thousandths inch. The above-mentioned test clip may be used to make electrical connections with each of the leads of a DIP package for signal testing (examination) and/or signal injecting (into the integrated circuit) purposes while the integrated circuit package is in usual mounting and/or use circumstances.
As it is used herein, the term or designation LCC is intended to encompass or to include leaded chip carriers or chip carrier packages that typically consist of one or more circuit chips mounted on a lead frame and encapsulated within an electrically non-conductive encapsulating medium. In one exemplary type the encapsulating medium is of a plastic or plastic-like material--hence the designation PLCC for plastic leaded chip carrier.
An exemplary PLCC is one identified as an "FN plastic chip carrier package" manufactured by Texas Instruments. Such PLCC is of generally square shape in top plan view and may have from 20 to 68 terminals or leads arranged in four equal groups respectively along or proximate to each side of the package. For example, the 20-lead model has five leads per side. The leads are positioned on 0.050 inch (1.27 mm) centers along each side and each lead has a side portion exposed at the side of the package and a bottom portion exposed at the bottom of the package. Such PLCC may be mounted on the surface of a printed circuit board using a soldering technique to attach mechanically and electrically each lead (at the bottom portion thereof) to a respective solder land on the printed circuit board.
Other PLCC's may have, for example, from about 20 to about 124 total leads arranged at or proximate to respective sides of the PLCC. Although the FN PLCC mentioned above has a generally square configuration in plan view, other PLCC's may be of rectangular shape not necessarily square.
Relative to the space and size requirements for a conventional DIP integrated circuit package, in a given space or area a PLCC may have a larger number of circuits and leads or terminals, this being due, at least in part, to the locating of leads along all four sides of the PLCC and the ability to narrow the spacing between leads in a PLCC relative to the wider spacing required in a conventional DIP package. For a number of reasons, such as surface mounting capability, close positioning of leads, and heat producing and/or tolerance characteristics of PLCC's, PLCC's can be mounted on a printed circuit board in relatively closely packed relationship with respectively adjacent PLCC's being spaced apart, for example, by 0.035 inch. Thus, using PLCC's, the capacity, e.g. in number of circuits, memory, etc. of a printed circuit board of a given size ordinarily would be larger than the capacity of such a printed circuit board employing conventional DIP integrated circuits.
As with DIP integrated circuit packages, it would be desirable to have a test clip that may be used to make electrical connections with each of the leads of the PLCC for signal testing and/or signal injecting purposes especially while the PLCC is in usual mounting and/or use circumstances. Because the leads are located along each of the four sides of the PLCC, prior test clips for DIP packages generally could not be used effectively even if appropriately sized since they would permit electrical connections with leads at only two opposed sides of the PLCC. There also may be a problem with interference between such prior test clips and an adjacent PLCC spaced, say 0.035 inch, from the PLCC to be tested.